Generally, in a fabrication line of a semiconductor, a liquid crystal display or the like, a gas reaction apparatus for performing various processes by introducing a source gas into a reaction chamber is utilized. For example, as for a film forming apparatus for forming an insulation thin film on a surface of a substrate to be processed such as a semiconductor wafer or the like, a chemical vapor deposition apparatus (CVD apparatus) for performing a film formation by a gas reaction has been known. Recently, the CVD apparatus is used for forming a multi-component metal oxide thin film such as PZT (lead zirconate titanate).
Generally, since an organic metal compound, which is a source material of a thin film such as PZT or the like, is solid at room temperature under atmospheric pressure, it is necessary to gasify this kind of a solid source material to supply it into a processing chamber to be used in the CVD apparatus. In this case, the solid source material is dissolved into a liquid by using a proper solvent (referred to as a solution source), and vaporized in a vaporizer to be supplied into the processing chamber. Such a source supply method is referred to as a solution vaporizing method. The solution vaporizing method has been actively studied and developed as a promising gasifying method capable of substituting a bubbling method or a solid sublimation method (e.g., see Japanese Patent Laid-open Application No. 7-94426).
Here, an example of forming a ternary metal oxide thin film by the solution vaporizing method will now be discussed. FIG. 10 is a schematic diagram showing an entire conventional gas reaction apparatus (film forming apparatus). As shown in FIG. 10, in a film forming apparatus 100, source material solutions, which are different from each other, are stored in source vessels divided into plural systems, respectively. For example, these source vessels are formed of a source vessel 101a for storing a lead based source material solution; a source vessel 101b for storing a zirconium based source material solution; and a source vessel 101c for storing a titanium based source material solution.
The source material solutions are respectively extracted into supply lines 103a, 103b and 103c to be flown through a main line 107 via respective flow rate controllers 105a, 105b and 105c by a pressurized gas A supplied through a force feed gas line 102. A carrier gas B such as a nonreactive gas (e.g., He, Ar or the like) or the like is supplied into the main line 107 through a flow rate controller 115. The source material solutions are mixed with the carrier gas in the main line 107, and thus transferred to a vaporizer 110 in a gas-liquid mixed state. Further, there is prepared a solvent vessel 101d for accommodating therein a solvent, e.g., butyl acetate, octane or THF (tetrahydrofuran). In the same manner, the solvent accommodated in the solvent vessel 101d is extracted to the supply line 104 by the pressurized gas A to be flown into the main line 107 through a flow rate controller 106.
A nozzle 111 is disposed at the vaporizer 110, to which the main line 107 is connected. Further, a carrier gas C is supplied to the nozzle 111 through a line 108 via a flow rate controller 109. At the nozzle 111, there is provided a nozzle port of a double tube structure. For example, the solution source materials supplied into an inner tube are sprayed into a vaporizing chamber 112 by the carrier gas C supplied into an outer tube. Here, a nozzle part is cooled below a room temperature to prevent the solvent having a low vaporization temperature from being vaporized first since a vaporization temperature of the solvent to be used is different from that of the source material itself, generally.
An inner surface of the vaporizer 112 corresponds to a vaporizing surface 112a for vaporizing the source material, and is heated to about, e.g., 200° C. Misty solution source materials ejected from the nozzle 111 collide with the vaporizing surface 112a to be vaporized instantaneously to become a source gas in the vaporizing chamber 112. The source gas is drained from a gas draining port 113 through a filter 114 to be supplied into a processing chamber 121 of a film forming apparatus main body 120 through a gas transporting line 116. The gas transporting line 116 is heated such that the source gas passing therethrough is not solidified or liquefied.
In the processing chamber 121, there are disposed a showerhead 122 to which the gas transporting line 116 is connected; and a susceptor 123 for mounting thereon a substrate W to be processed. An oxidizing gas, such as O2, N2O, NO2 or the like, which reacts with the source gas in the processing chamber 121, is supplied into the showerhead 122 through a reaction gas supply line 117. In the processing chamber 121, a thin film is formed on the substrate to be processed W by reactions between the source gas and the oxidizing gas.
However, in the conventional film forming apparatus 100, the gas transporting line 116 between the vaporizer 110 and the processing chamber 121 is long so that particles are likely to be produced in the source gas, or a supply amount of source gas is fluctuated, thereby deteriorating the uniformity in a film composition or a film thickness.
Further, an inside of the entire gas transporting line 116 must be heated to a temperature higher than a vaporization temperature of the source and at the same time lower than a decomposition temperature thereof, such that the source gas is not solidified or liquefied during the transportation. In this case, since a heating unit and a temperature control unit are required, the overall structure gets complicated. Moreover, the vaporizer 110, the gas transporting line 116 and the processing chamber 121 need to be heated individually, resulting in an increase of power consumption. In addition, the vaporizer 110 and the gas transporting line 116 need to be equipped with a heating unit, so that the entire apparatus becomes large-scaled.